1. Field of the Invention
This invention relates to an implantable energy storage arrangement for a medical implant, the energy storage arrangement comprising a rechargeable storage for electrical energy and a unit for controlling the charging process via an actuator in the charging path. This invention further relates to a process for operating an implantable energy storage arrangement for a medical implant, said energy storage arrangement comprising a rechargeable storage for electrical energy, wherein during normal operation the charging process is controlled by means of a control unit via an actuator in the charging path.
2. Description of Related Art
Energy storage arrangements and processes of the aforementioned type are described, for example, in commonly owned, co-pending U.S. patent application Ser. No. 09/311,566 which is hereby incorporated by reference, and U.S. Pat. Nos. 5,411,537, 5,702,431 and 5,713,939. Conventionally, the implantable energy storage arrangements are recharged transcutaneously via an inductive path by means of an external charging device. The charging device conventionally is controlled by measuring the charging current and the voltage of the storage by means of a control unit and by converting the same into the corresponding control pulses for a switch in the charging circuit, wherein a suitable charging program is used.
When the energy storage is in operation, two undesirable operating states can occur: On the one hand, overcharging of the battery can occur if the charging process is not terminated at the proper time, which may lead to gas evolution with subsequent destruction of the storage. On the other hand, when charging of the storage is not done on time, the storage voltage may drop to values which are below a minimum operating voltage which is necessary for defined operation or optionally for limited function of the implant which is to be supplied by the energy storage. In the latter case, the storage voltage may possibly drop to such an extent that even sufficient voltage supply of the implant-side electronics to control the charging process is no longer ensured. Often, the control electronics comprise a microprocessor system in which, in the case of undervoltage, wrong logic operations can occur or the contents of volatile memories can be lost. Thus, in the case of undervoltage, in these systems proper charge control is no longer ensured; this can lead to the charging path being switched to high resistance by a microprocessor malfunction when it enters the undervoltage range, whereby charging of the storage is permanently prevented.
A primary object of this invention is to devise an implantable energy storage arrangement for a medical implant and a process for its operation, wherein safe recharging of the energy storage is possible even when the storage is completely discharged or has been discharged at least to such an extent that the storage voltage has dropped below the normal voltage range for the control unit.
This object is achieved in conformity with the invention by an implantable energy storage arrangement for a medical implant, with a rechargeable storage for electrical energy and a unit for controlling the charging process via an actuator in the charging path, characterized in that there is a means which can be externally activated to bypass the actuator. The above object furthermore is achieved in conformity with the invention by a process for operating an implantable energy storage arrangement for a medical implant, with a rechargeable storage for electrical energy, in normal operation the charging process being controlled by means of a control unit via an actuator in the charging path, wherein when it is not possible to charge the storage via the actuator due to overly low storage voltage, a bypass means provided in the implantable energy storage arrangement is activated from the outside to bypass the actuator.
In this approach in accordance with the invention, it is advantageous that even when discharge of the storage has progressed far or even the storage has been completely discharged, i.e., at very low storage voltages, the rechargeability of the storage is ensured at any time by preventing blockage of the charging path due to malfunction of the control unit caused by the undervoltage, which blockage is prevented by having the possibility of means of bridging the actuator element in the charging path by external actuation of the bridging unit.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawing which, for purposes of illustration only, shows an embodiment in accordance with the present invention.